Themis directs T cell exhaustion by promoting PD-1 signaling and regulating expression of transcription factors TCF-1 and TOX

T cell exhaustion is a protective mechanism during chronic viral infections, but it can impair anti-tumor immunity. Themis, a T cell-specific protein, is critical for CD8+ T cell homeostasis, cytokine responsiveness, and anti-Listeria responses. In Themis-deficient mice infected with LCMV C13, a chronic virus, we observed severe lung injury and premature death. Single-cell analysis revealed that Themis-deficient effector CD8+ T cells, while producing higher levels of TNF and IFN-?, were impaired in population expansion due to poor cell sustainability. Biochemical studies showed that Themis binds PD-1, promoting PD-1 phosphorylation and SHP-2 recruitment. Beyond its role in restraining effector T cell function, Themis is essential for the development of Tpex cells by promoting TCF-1 expression and driving transcriptional and epigenetic changes. Moreover, Themis supports TOX and PD-1 expression, ensuring the maintenance of terminally exhausted T cells (Tex). This study reveals the multifaceted roles of Themis in the progression of T cell exhaustion. Overall design: Primary murine tissues were collected from co-transfer p14 mice, with tissues isolated at different time points following infection with LCMV-clone 13. A total of 4 single-cell samples were prepared, consisting of CD4+ T cells from spleen or lung tissues, with both wild-type (WT) and knockout (KO) groups, at 5 days post-infection (dpi). The isolated single-cell suspensions were processed using the DNBSEQ platform, which was run on the DNBelab C4 portable single-cell system (BGI). This system facilitates high-throughput cell capture and gene expression profiling.